(a) Field of the Invention
The present invention relates to an ultrahigh frequency In-phase/Quadrature-phase (I/Q) transmitter/receiver using a multi-stage harmonic mixer.
(b) Description of the Related Art
A typical In-phase/Quadrature-phase (I/Q) receiver includes a direct conversion receiver and a receiver using a harmonic mixer. The structure of the receiver will be described in detail with reference to FIGS. 1 and 2.
FIG. 1 is a configuration diagram that illustrates a typical direct conversion receiver.
Referring to FIG. 1, the direct conversion receiver includes a voltage controlled oscillator (VCO) and a phase looked loop (PLL). The PLL stabilizes the VCO, and the VCO oscillates a frequency. The frequency output from the VOC may be same to an input signal (RFin) of the direct conversion receiver or may be different from the input signal (RFin) as much as an intermediate frequency.
The direct conversion receiver has a structure that down-converts a frequency signal, which is different from the input frequency as much as the VCO frequency, to an I-path and a Q-path when the output frequency of the VCO is applied to a mixer after passing through a circuit for dividing a signal to I/Q.
The direct conversion receiver may be realized with simple blocks if the VCO frequency is generated to be equal or similar to the input signal.
However, it is very difficult to design a super high frequency PLL of a super high frequency integrated circuit (IC) for generating a high frequency like a super high frequency input signal or for stabilizing the generated high frequency. The direct conversion receiver of FIG. 1 is not proper for such a super high frequency integrated circuit. Furthermore, the direct conversion receiver of FIG. 1 has characteristic that the phase noise of the oscillator becomes deteriorated quickly as a frequency of the oscillator increases. Accordingly, the direct conversion receiver of FIG. 1, which uses a high frequency oscillator, is not proper from a noise point of view.
FIG. 2 is a configuration diagram that illustrates a receiver using a harmonic mixer.
Unlike the direct conversion receiver of FIG. 1, a Vlo frequency becomes a half a RFin frequency in a receiver including a harmonic mixer, as shown in FIG. 2. Accordingly, frequency generation is comparatively easier. Furthermore, the receiver using the harmonic mixer has a structure reducing a phase noise.
However, in order to design an I/Q structure of FIG. 2, a 45° generator is required. It is not easy to accurately generate 45° phase frequencies from the Vlo frequency. As a result, a noise is generated in the receiver.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.